1
„Vector Control(Field Oriented Control, Direct Torque Control)“
Referents:Prof. Dr.‐Ing. Ralph Kennel
([email protected])Technische Universität München
Arcisstraße 2180333 München
Germany
2
of Field Oriented Control (FOC)
as well as Direct Torque Control (DTC)
is to operate AC machines/motors
directly by the physical law of Lorentz force
(that means, the torque is produced
by an electrical current in a magnetic field)
magnetic field
and armature current (for torque production)
are controlled separately and independently
The General Idea
3
Force Production in Synchronous Machines
… in principle the magnetic conditions in a synchronous machines are equal… to DC machines
B
If
B
4
… even in high speed condition the mechanical motion is so slowthat Maxwell‘s equations can be applied in the same way
(there is no energy radiation – there is no Displacement Current)
B
If
B
Force Production in Synchronous Machines
5
… in DC machines the excitation magnetic field does not move in space… the coordinate system is fixed in space as well
this is „automatically“ field orientation
B
If
B
coordinate axis in field direction(field winding)
d-coordinate
Force Production in Synchronous Machines
6
… in DC machines the excitation magnetic field does not move in space… the coordinate system is fixed in space as well
this is „automatically“ field orientation
B
If
B
coordinate axis in „armature“-direction(armature winding)
q-coordinate
Force Production in Synchronous Machines
7
B
If
B
… in synchronous machines the excitation magnetic field is fixed to the rotor… it is possible to define the coordinate system fixed to the rotor as well
this is called „field orientation“
coordinate axis in field direction(field winding)
d-coordinate
Force Production in Synchronous Machines
8
B
If
B
… in synchronous machines the excitation magnetic field is fixed to the rotor… it is possible to define the coordinate system fixed to the rotor as well
this is called „field orientation“
coordinate axis in „armature“-direction(armature winding)
q-coordinate
Force Production in Synchronous Machines
9
B
If
B
… in synchronous machines the excitation magnetic field is fixed to the rotor… it is possible to define the coordinate system fixed to the rotor as well
this is called „field orientation“
Force Production in Synchronous Machines
… in that case it is possible to applythe same equations
as in DC machines
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voltage and frequency are irrelevant
for this type of control
… under this assumption
any AC machine/motor
behaves like a DC motor
The General Idea
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constanttorque
constantpower
Torque and Power Characteristics of Electrical Machines
12
constanttorque
constantpower
base speedrange
field weakeningrange
Torque and Power Characteristics of Electrical Machines
13
Referents:Prof. Dr.‐Ing. Hans‐Georg Herzog
([email protected])Prof. Dr.‐Ing. Ralph Kennel
([email protected])Technische Universität München
Arcisstraße 2180333 München
Germany
characteristic
„Vector Control(Field Oriented Control, Direct Torque Control)“
14
(Linear) Control Loop
controllercontrolling
elementcontrolled
system
control error e(t)
advantages of (linear) control loops
• well accepted compromise between stability and dynamics
• simple optimization procedures (step response …)
• acceptable robustness against parameter variations
• (limited) implicit linearization auf non-linear components
15
Step Responses
overshoot
compromise
lower dynamics
16
Cascade Structure
- --
Drehzahl-regelung
Drehmoment-/StromRegelung
M3~
i
Lageregelung
Lagegeber
Tacho
Kommutierungssignale
s*
s
n* i*
n
position controllerspeed
controller
torque/currentcontroller
commutation signals
tacho generator
position encoder
servomotor
cascaded control with 3 control loops
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… controls the magnetic fieldby a current (Ampère’s law) in d-direction and
… and the torqueby a quadrature (armature) current in q-direction
the position of the magnetic field is neededto perform FOC
this can be obtained by a position sensoror so-called “sensorless control”
Field Oriented Control (FOC)
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-
Feldschwächung
- -
-
M-Regler Strom-Regler
Feld-Regler
Ma-schinen-modell
ej
e-j
e-j
M3~
i
u
Encoder
n* i*q
i*d*
for asynchronousmachines
field weakening field controller
speedcontroller
currentcontrollers
machine
model
for synchronousmachines
Field Oriented Control (FOC)
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Field Oriented Control
19
• Rotor flux orientation
• PI-controllers
• Cascaded structure
• Limitation in the dynamic response
• Average voltage control
*
sdi
*
sqi
sdi
sqi
*
sdv
*
sqv
dq
abc
*
sv
*
sv
*v*
bv
*
cv
1S
2S
3S
s
r
*
r
*w
w
PI
wPI
diPI
qiPI
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… controls the magnetic field
by the stator voltage (Faraday’s law)
… and the torque
by the stator current (Lorentz force)
DTC does not need a position/speed sensor
unless position or speed have to be controlled
Direct Torque Control (DTC)
21
21
*ww
*T
T *
Direct Torque Control
• Stator flux and torque tontrol
• Hysteresis controllers
• No current regulation
• No modulator
• Switching table
22
22
• magnetic flux is integral of stator voltage
• magnetic flux moves in direction of stator voltage
3v
3v
s k
s k 1s k
1s k
Results DTC: Stator flux distortion
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• Stator flux path control
• Current waveform
• Number of commutations
• Direct Self Control (DSC)
Results DTC: Torque and flux hysteresis bands
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increasing
24
24
• Tn=20[Nm],w=1000[RPM]
Final Compariosn: Steady state
0.9 0.92 0.94 0.96 0.98 10
10
20
30
Tor
que
[Nm
]
0.9 0.92 0.94 0.96 0.98 10
10
20
30
Tor
que
[Nm
]
0.9 0.92 0.94 0.96 0.98 10
10
20
30
Tor
que
[Nm
]
0.9 0.92 0.94 0.96 0.98 10
10
20
30
Time [s]
Tor
que
[Nm
]
FOC
DTC
PTCk1
PTCk2
25
25
0.9 0.92 0.94 0.96 0.98 1-30
-15
0
15
30
Am
plitu
de [
A]
0.9 0.92 0.94 0.96 0.98 1-30
-15
0
15
30
Am
plitu
de [
A]
0.9 0.92 0.94 0.96 0.98 1-30
-15
0
15
30
Am
plitu
de [
A]
0.9 0.92 0.94 0.96 0.98 1-30
-15
0
15
30
Time [s]
Am
plitu
de [
A]
• Tn=20[Nm],w=1000[RPM]
FOC
DTC
PTCk1
PTCk2
THD
2%
9.5%
6%
3.5%
Final Compariosn: Steady state
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26
0.9 0.92 0.94 0.96 0.98 1-400
-200
0
200
400
Vol
tage
[V
]
0.9 0.92 0.94 0.96 0.98 1-400
-200
0
200
400
Vol
tage
[V
]
0.9 0.92 0.94 0.96 0.98 1-400
-200
0
200
400
Vol
tage
[V
]
0.9 0.92 0.94 0.96 0.98 1-400
-200
0
200
400
Time [s]
Vol
tage
[V
]
• Tn=20[Nm],w=1000[RPM]
FOC
DTC
PTCk1
PTCk2
Final Compariosn: Steady state
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0.69 0.7 0.71 0.72 0.73-5
0
5
10
15
20
Time [s]
Torq
ue [N
m]
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• Torque reference step of 15 [Nm]
Final comparison: Torque response
FOC
DTC
FOC
DTC
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28
• Flux reference step of 0.19 [Wb]
0.4 0.45 0.5 0.55 0.6 0.65 0.70.65
0.7
0.75
0.8
0.85
Time [s]
Flux
[Wb]
FOCDTC
Final comparison: Stator flux response
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29
• Stator current behavior
FOC DTC
Final comparison: Stator flux response
30
30
• High starting current
Final comparison: Starting without limitation
0 0.1 0.2 0.3-70
-35
0
35
70
Am
plitu
de [
A]
0 0.1 0.2 0.3-70
-35
0
35
70
Am
plitu
de [
A]
0 0.1 0.2 0.3-70
-35
0
35
70
Am
plitu
de [
A]
0 0.1 0.2 0.3-70
-35
0
35
70
Time [s]
Am
plitu
de [
A]
FOC
DTC
PTCk1
PTCk2
-37.8 [A]
-62.4 [A]
65 [A]
64.3 [A]
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31
• Stator flux
FOC DTC
Final comparison: Starting without limitation
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32
• Limited stator current
0 0.1 0.2 0.3-40
-20
0
20
40
Am
plitu
de [
A]
0 0.1 0.2 0.3-40
-20
0
20
40
Am
plitu
de [
A]
0 0.1 0.2 0.3-40
-20
0
20
40
Am
plitu
de [
A]
0 0.1 0.2 0.3-40
-20
0
20
40
Time [s]
Am
plitu
de [
A]
FOC
DTC
PTCk1
PTCk2
Final comparison: Starting with current limitation
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33
• Stator flux
FOC DTC
Final comparison: Starting with current limitation
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any AC drive under FOC (or DTC) behaveslike a synchronous drive
or a DC motor with speed/position control
… under speed control a real speed is kept constantaccording to the speed reference
under any load until maximum torque… when exceeding maximum torque
the drive is not stopping at standstill (breakdown),but reducing speedas long as the required torque can be provided
characteristicAC machine with speed control
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an electrical machine with inverter supply
and speed control
always provides
the characteristic of a synchronous machine
… independant on the type
of the respective electrical machine
characteristicAC machine with speed control
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speed
torq
ue
motor operationPel > 0
Pmech< 0
generator operationPel < 0
Pmech> 0
… variations of supply voltageresult in a shift of the characteristic … but vertically only
… variations of supply frequencyresult in a shift of the characteristic horizontally
load characteristic
operation point
… that is exactly, what speed control performswhen speed reference varys
characteristicAC machine with speed control
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speed
torq
ue
motor operationPel > 0
Pmech< 0
generator operationPel < 0
Pmech> 0
… here the characteristicsare arbitrary definitions as well
… the transition frommotor to generator operation
or vice versavirtually happens „automatically“
… as soon asthe operation point changes
from the first quadrantto the fourth quadrant
(or vice versa)
characteristicAC machine with speed control
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source : SIEMENS
characteristic of (synchronous) drivewith speed control
thermal limitation
limitation by maximum stator voltage
limitation by maximum stator current
… unfortunately in most data sheetsthe 1. quadrant is presented only
characteristicAC machine with speed control
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Referents:Prof. Dr.‐Ing. Hans‐Georg Herzog
([email protected])Prof. Dr.‐Ing. Ralph Kennel
([email protected])Technische Universität München
Arcisstraße 2180333 München
Germany
advantages in comparison to U/f Control
„Vector Control(Field Oriented Control, Direct Torque Control)“
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advantages of FOC or DTCin comparison to U/f Control
that FOC or DTC are feedback control schemes
U/f control is a feedforward control scheme
FOC and DTC can react on (torque) disturbances
– U/f control cannot
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DC SM ASM
Advantages
Disadvantages
- Simple control
- interior ventilation
simple to realize
- high protection standard
- small size
- maintenance free
- low inertia
- high torque
even at standstill
- high dynamics
- losses in the stator
- high protection standard
- maintenance free
- high overload capability
- low cost
- high torque
even at standstill
- high speed range
- low protection standard
- mechanical wear
(brushes, collector)
- current limitation
- standstill
(collector segments)
- high speed
(commutation)
- maximum terminal
voltage of 200 V
(transformer needed)
- losses in the rotor
(heat transfer via shaft)
- high cost
- limited speed range
- limited overload
capability
(demagnetizion)
- harmonic losses
mainly in the rotor
(heat transfer via shaft)
- high inertia
- field current needed
(losses, size,
bigger inverter)
- complex control
- Parameter depending
control
Comparison of Different Electrical Machines
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Thank You !!!
Any Questions ?
Prof. Dr.-Ing. Ralph Kennel
Technische Universität München
Electrical Drive Systems and Power Electronics
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